Incoherent tunneling and topological superconductivity in twisted cuprate bilayers

Abstract

Twisting two monolayers of a high-Tc cuprate superconductor can engender a chiral topological state with spontaneously broken time-reversal symmetry T. A crucial ingredient required for the emergence of a gapped topological phase is electron tunneling between the CuO2 planes, whose explicit form (in an ideal sample) is dictated by the symmetry of the atomic orbitals. However, a large body of work on interlayer transport in cuprates indicates the importance of disorder-mediated incoherent tunneling, which evades symmetry constraints present in an idealized crystal. This arises even in the cleanest single-crystal samples through oxygen vacancies, in layers separating the CuO2 planes, introduced to achieve the hole doping necessary for superconductivity. Here we assess the influence of incoherent tunneling on the phase diagram of a twisted bilayer and show that the model continues to support a fully gapped topological phase with broken T. Compared to the model with a constant, momentum conserving interlayer coupling, the extent of the topological phase around the 45° twist decreases with increasing incoherence, but remains robustly present for parameters likely relevant to Bi2Sr2CaCu2O8+δ.